US4853080A - Lift-off process for patterning shields in thin magnetic recording heads - Google Patents
Lift-off process for patterning shields in thin magnetic recording heads Download PDFInfo
- Publication number
- US4853080A US4853080A US07/284,166 US28416688A US4853080A US 4853080 A US4853080 A US 4853080A US 28416688 A US28416688 A US 28416688A US 4853080 A US4853080 A US 4853080A
- Authority
- US
- United States
- Prior art keywords
- layer
- depositing
- resist material
- etching
- transfer layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Images
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
- G11B5/3163—Fabrication methods or processes specially adapted for a particular head structure, e.g. using base layers for electroplating, using functional layers for masking, using energy or particle beams for shaping the structure or modifying the properties of the basic layers
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F4/00—Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/004—Photosensitive materials
- G03F7/09—Photosensitive materials characterised by structural details, e.g. supports, auxiliary layers
- G03F7/094—Multilayer resist systems, e.g. planarising layers
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
- H05K3/14—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using spraying techniques to apply the conductive material, e.g. vapour evaporation
- H05K3/143—Masks therefor
Definitions
- the present invention relates generally to processes of fabricating thin film recording heads, and more particularly to a lift-off process for patterning shields in such recording heads.
- Amorphous magnetic alloy shield materials are generally incompatible with such plating processes.
- three possible alternative process types are possible. These include ion etching, chemical etching and lift-off processes.
- a lift-off process is a highly desirably process to implement the pattering of amorphous shield materials. Accordingly, the present invention provides for a lift-off process for patterning bottom shields which are employed in thin film magnetic recording heads.
- the lift-off process comprises the steps of providing a substrate and depositing a first layer of resist material on one surface of the substrate. A transfer layer is deposited on top of the first layer of resist material and a second layer of resist material is deposited on top of the transfer layer.
- the second layer of resist material is then patterned and the patterned structure is etched to form a mask structure wherein the transfer layer overhangs the first layer of resist.
- An amorphous magnetic alloy material is then deposited on the exposed surface of the substrate. Finally, the resist materials, transfer layer and unwanted amorphous alloy are removed.
- the step of depositing the first layer of resist material includes heating the material to a predetermined elevated temperature of about 120 degrees Celsius.
- the transfer layer is typically sputtered onto the underlying layer at a minimum pressure of 10 milliTorr.
- the second layer of resist material is typically spun onto the top surface of the transfer layer and photolithographically patterned using a negative image mask.
- the step of etching the patterned structure comprises the steps of etching through the exposed transfer layer using carbon tetrafluoride plasma, etching a vertical wall trough in the first layer of resist material in an oxygen-carbon tetrafluoride plasma, etching the first layer of photoresist to form an overhang structure using oxygen-sulfur hexafluoride plasma, and cleaning the the exposed surfaces using an argon-oxygen-carbon tetrafluoride plasma.
- An adhesion layer is deposited by sputtering prior to the deposition of the amorphous magnetic alloy shield.
- the adhesion layer typically comprises a layer of hafnium.
- the step of removing the layer of resist, transfer layer and excess amorphous alloy is accomplished by ultrasonic agitation in acetone.
- the above processing steps are highly reproducible since they employ dry processing technology, namely reactive ion etching and sputtering.
- the processing is compatible with multi-wafer batch processes. Tapered sidewall profiles of the shields are achieved which enhance the reliability of subsequently deposited metallization. Also, contrary to chemical etching, narrow linewidths, such as are required for photolithographic alignment marks, are reproduced by the lift-off process.
- the use of hafnium enhances adhesion of the amorphous magnetic material to the underlying substrate.
- the 120 degree Celsius baking temperature of the first resist layer enables the lift-off process to be performed in acetone while simultaneously eliminating resist reflow during subsequent processing.
- FIGS. 1a-c illustrate the process steps in fabricating shields comprising amorphous magnetic alloy material in accordance with the principles of the present invention.
- a substrate 20 which may be a nonconducting oxide material, such as alumina, or the like, is provided, onto which is deposited a first layer of photoresist 22.
- a photoresist 22 Typical of such a photoresist is type AZ4210 manufactured by Azoplate, or the like.
- the first layer of photoresist 22 is deposited to a thickness of about 2.5 micrometers.
- a second layer of photoresist 26 is then deposited on the exposed surface of the transfer layer 24.
- the first layer of photoresist 22 is spun on in a conventional manner and baked, or heated on a hotplate, for example, to a temperature of 120 degrees Celsius for a period of 5 minutes.
- the transfer layer 24 is vacuum deposited under low stress conditions wherein the stress is less than about 1 ⁇ 10 9 dynes per square centimeter. Such conditions typically require that the pressures used in the deposition step are greater than a minimum pressure of about 10 milliTorr (mT).
- the second layer of photoresist 26 is spun on in a conventional manner and baked, or heated on a hotplate, for example, at a temperature of 85 degrees Celsius for a period of 5 minutes.
- the second layer of photoresist 26 is then patterned in a conventional manner using a photolithographic process commonly employed in wafer processing.
- a negative image mask is employed in the patterning step.
- the patterned structure is then etched using a reactive ion etching procedure.
- This procedure comprises the steps of etching through the exposed transfer layer using carbon tetrafluoride plasma, etching a vertical wall trough in the first layer of photoresist 22 in an oxygen-carbon tetrafluoride plasma, etching the first layer of photoresist 22 to form an overhanging transfer layer using using oxygen-sulfur hexafluoride plasma, and cleaning the the exposed surfaces using an argon-oxygen-carbon tetrafluoride plasma.
- FIG. 1a illustrates the structure achieved after the patterning and development of the second layer of photoresist 26 has been accomplished.
- FIG. 1b it illustrates the structure achieved after the above-described etching procedure has been accomplished.
- the extent of the undercut below the transfer layer 24 achieved by the etching procedure is about 4 pmicrometers.
- This etched structure is placed in a sputtering chamber having a sputtering source 28, wherein an adhesion layer 30 (shown in FIG. 1c), which may comprise hafnium, or the like is deposited on the exposed surface of the substrate 20.
- the layer of hafnium is typically deposited to a thickness of about 25 nanometers.
- an amorphous magnetic alloy material 32 shown in FIG. 1c is sputter deposited on top of the adhesion layer 30.
- the amorphous alloy material 32 is deposited with a stress level less than 10 9 dynes per square centimeter. A deposition pressure of about 3.4 mT provides such a stress state.
- Typical of such an amorphous magnetic alloy material 32 is Cobalt hafnium Niobium (CoHfNb), and it is deposited to a thickness of about 2 micrometers.
- the sidewall structure of the sputtered amorphous magnetic alloy material 32 has a gradually sloping profile which enhances a subsequently deposited conductor metallization.
- FIG. 1c shows the structure achieved after deposition of the amorphous magnetic alloy material 32 and removal of the masking and residue materials.
- the above-described process provides for tapered sidewalls of the amorphous magnetic alloy material 32 which have a maximum slope of about 45 degrees.
- the transfer layer is deposited with a stress less than about 1 ⁇ 10 9 dynes per square centimeter. This is accomplished by sputtering at a minimum system pressure of 10 mT.
- a sputtering source 28 is shown in FIG. 1b and illustrates that deposition of the amorphous magnetic alloy material 32 does not impinge upon the vertical sidewalls formed in the first layer of photoresist 22. This, of course, is achieved by the overhanging mask structure created by the transfer layer 24. It is important that the deposition of the amorphous magnetic alloy material 32 does not impinge on the sidewalls of the transfer layer 24, since such impingement would create an unwanted build up of the amorphous magnetic alloy material. Such a build up would cause deleterious effects in the finalized recording head, as is well-known in the art. In particular, an undesirable ridge is left around the periphery of the pattern.
- the 120 degree Celsius baking temperature of the first layer of photoresist 22 is necessary to enable the lift-off process to be performed in acetone while simultaneously eliminating resist reflow during subsequent processing.
- the above processing steps are highly reproducible since they employ dry processing technology, namely reactive ion etching and sputtering.
- the processing is compatible with multi-wafer batch processes. Tapered sidewall profiles of the shields are achieved which enhance the reliability of subsequently deposited conductor metallization. Also, narrow linewidths, such as those required for photolithographic alignment are reproduced by this lift-off process.
- the use of hafnium enhances adhesion of the amorphous magnetic material to the underlying substrate.
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Architecture (AREA)
- Structural Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Manufacturing & Machinery (AREA)
- Magnetic Heads (AREA)
Abstract
Description
Claims (24)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US07/284,166 US4853080A (en) | 1988-12-14 | 1988-12-14 | Lift-off process for patterning shields in thin magnetic recording heads |
EP19890312459 EP0373793A3 (en) | 1988-12-14 | 1989-11-30 | Lift-off process for patterning shields in thin magnetic recording heads |
JP1323670A JPH02218010A (en) | 1988-12-14 | 1989-12-13 | Manufacture of thin film magnetic recording head |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US07/284,166 US4853080A (en) | 1988-12-14 | 1988-12-14 | Lift-off process for patterning shields in thin magnetic recording heads |
Publications (1)
Publication Number | Publication Date |
---|---|
US4853080A true US4853080A (en) | 1989-08-01 |
Family
ID=23089134
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US07/284,166 Expired - Fee Related US4853080A (en) | 1988-12-14 | 1988-12-14 | Lift-off process for patterning shields in thin magnetic recording heads |
Country Status (3)
Country | Link |
---|---|
US (1) | US4853080A (en) |
EP (1) | EP0373793A3 (en) |
JP (1) | JPH02218010A (en) |
Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5185055A (en) * | 1989-05-12 | 1993-02-09 | Xaar Limited | Method of forming a pattern on a surface |
US5302461A (en) * | 1992-06-05 | 1994-04-12 | Hewlett-Packard Company | Dielectric films for use in magnetoresistive transducers |
US5527663A (en) * | 1991-03-01 | 1996-06-18 | Teijin Seiki Co., Ltd. | Method of manufacturing a medium having a magnetic pattern |
US5804085A (en) * | 1997-01-30 | 1998-09-08 | Quantum Corporation | Process for producing a pole-trimmed writer in a magnetoresistive read/write head and a data transducer made thereby |
US6469877B1 (en) | 1999-06-15 | 2002-10-22 | Read-Rite Corporation | Spin valve device with improved exchange layer defined track width and method of fabrication |
US20030150898A1 (en) * | 1997-06-10 | 2003-08-14 | Agere Systems Inc. | Micromagnetic device for power processing applications and method of manufacture therefor |
US6649422B2 (en) | 1999-06-22 | 2003-11-18 | Agere Systems Inc. | Integrated circuit having a micromagnetic device and method of manufacture therefor |
US6696744B2 (en) | 1997-06-10 | 2004-02-24 | Agere Systems, Inc. | Integrated circuit having a micromagnetic device and method of manufacture therefor |
US20040109263A1 (en) * | 2002-03-29 | 2004-06-10 | Shoichi Suda | Manufacturing process of a magnetic head, magnetic head, pattern formation method |
US20080299303A1 (en) * | 2007-04-26 | 2008-12-04 | Shinko Electric Industries Co., Ltd. | Method of manufacturing optical device |
US20110185353A1 (en) * | 2010-01-27 | 2011-07-28 | Jack Matthew | Mitigating Problems Arising From Incompatible Software |
US20130214123A1 (en) * | 2012-02-16 | 2013-08-22 | Seiko Epson Corporation | Interference filter, optical module, and electronic apparatus |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5116719A (en) * | 1990-02-15 | 1992-05-26 | Seagate Technology, Inc. | Top pole profile for pole tip trimming |
DE4012823A1 (en) * | 1990-04-23 | 1991-11-14 | Thomson Brandt Gmbh | METHOD FOR PRODUCING A THIN FILM MAGNETIC TAPE HEAD |
JPH1083517A (en) * | 1996-09-10 | 1998-03-31 | Alps Electric Co Ltd | Thin-film magnetic head and its production |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4202914A (en) * | 1978-12-29 | 1980-05-13 | International Business Machines Corporation | Method of depositing thin films of small dimensions utilizing silicon nitride lift-off mask |
US4218532A (en) * | 1977-10-13 | 1980-08-19 | Bell Telephone Laboratories, Incorporated | Photolithographic technique for depositing thin films |
US4481071A (en) * | 1983-12-29 | 1984-11-06 | International Business Machines Corporation | Process of lift off of material |
US4533431A (en) * | 1983-01-13 | 1985-08-06 | Commissariat A L'energie Atomique | Process for producing conductors for integrated circuits using planar technology |
US4568411A (en) * | 1983-11-22 | 1986-02-04 | British Telecommunications Plc | Metal/semiconductor deposition |
US4710263A (en) * | 1985-09-11 | 1987-12-01 | Alps Electric Co., Ltd. | Method of fabricating print head for thermal printer |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS6022721A (en) * | 1983-07-16 | 1985-02-05 | Alps Electric Co Ltd | Thin film magnetic head |
JPH0695370B2 (en) * | 1984-03-08 | 1994-11-24 | 株式会社ケンウッド | Pattern forming method for thin film magnetic head |
JPS61107512A (en) * | 1984-10-31 | 1986-05-26 | Hitachi Ltd | Thin film magnetic head |
JPS6292216A (en) * | 1985-10-18 | 1987-04-27 | Seiko Epson Corp | Production of magnetic head |
JPS6394423A (en) * | 1986-10-07 | 1988-04-25 | Citizen Watch Co Ltd | Production of thin film magnetic head |
JPS63168810A (en) * | 1986-12-30 | 1988-07-12 | Alps Electric Co Ltd | Production of thin film magnetic head |
-
1988
- 1988-12-14 US US07/284,166 patent/US4853080A/en not_active Expired - Fee Related
-
1989
- 1989-11-30 EP EP19890312459 patent/EP0373793A3/en not_active Withdrawn
- 1989-12-13 JP JP1323670A patent/JPH02218010A/en active Pending
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4218532A (en) * | 1977-10-13 | 1980-08-19 | Bell Telephone Laboratories, Incorporated | Photolithographic technique for depositing thin films |
US4202914A (en) * | 1978-12-29 | 1980-05-13 | International Business Machines Corporation | Method of depositing thin films of small dimensions utilizing silicon nitride lift-off mask |
US4533431A (en) * | 1983-01-13 | 1985-08-06 | Commissariat A L'energie Atomique | Process for producing conductors for integrated circuits using planar technology |
US4568411A (en) * | 1983-11-22 | 1986-02-04 | British Telecommunications Plc | Metal/semiconductor deposition |
US4481071A (en) * | 1983-12-29 | 1984-11-06 | International Business Machines Corporation | Process of lift off of material |
US4710263A (en) * | 1985-09-11 | 1987-12-01 | Alps Electric Co., Ltd. | Method of fabricating print head for thermal printer |
Cited By (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5185055A (en) * | 1989-05-12 | 1993-02-09 | Xaar Limited | Method of forming a pattern on a surface |
US5527663A (en) * | 1991-03-01 | 1996-06-18 | Teijin Seiki Co., Ltd. | Method of manufacturing a medium having a magnetic pattern |
US5302461A (en) * | 1992-06-05 | 1994-04-12 | Hewlett-Packard Company | Dielectric films for use in magnetoresistive transducers |
US5804085A (en) * | 1997-01-30 | 1998-09-08 | Quantum Corporation | Process for producing a pole-trimmed writer in a magnetoresistive read/write head and a data transducer made thereby |
US6141183A (en) * | 1997-01-30 | 2000-10-31 | Matsushita-Kotobukie Electronics Industries, Ltd. | Process for producing a pole-trimmed writer in a magnetoresistive read/write head and a data transducer made thereby |
US6696744B2 (en) | 1997-06-10 | 2004-02-24 | Agere Systems, Inc. | Integrated circuit having a micromagnetic device and method of manufacture therefor |
US20030150898A1 (en) * | 1997-06-10 | 2003-08-14 | Agere Systems Inc. | Micromagnetic device for power processing applications and method of manufacture therefor |
US7021518B2 (en) | 1997-06-10 | 2006-04-04 | Agere Systems Inc. | Micromagnetic device for power processing applications and method of manufacture therefor |
US6469877B1 (en) | 1999-06-15 | 2002-10-22 | Read-Rite Corporation | Spin valve device with improved exchange layer defined track width and method of fabrication |
US6649422B2 (en) | 1999-06-22 | 2003-11-18 | Agere Systems Inc. | Integrated circuit having a micromagnetic device and method of manufacture therefor |
US20040109263A1 (en) * | 2002-03-29 | 2004-06-10 | Shoichi Suda | Manufacturing process of a magnetic head, magnetic head, pattern formation method |
US7244368B2 (en) * | 2002-03-29 | 2007-07-17 | Fujitsu Limited | Manufacturing process of a magnetic head, magnetic head, pattern formation method |
US20080299303A1 (en) * | 2007-04-26 | 2008-12-04 | Shinko Electric Industries Co., Ltd. | Method of manufacturing optical device |
US20110185353A1 (en) * | 2010-01-27 | 2011-07-28 | Jack Matthew | Mitigating Problems Arising From Incompatible Software |
US20130214123A1 (en) * | 2012-02-16 | 2013-08-22 | Seiko Epson Corporation | Interference filter, optical module, and electronic apparatus |
US9279925B2 (en) * | 2012-02-16 | 2016-03-08 | Seiko Epson Corporation | Interference filter, optical module, and electronic apparatus |
Also Published As
Publication number | Publication date |
---|---|
EP0373793A3 (en) | 1992-03-11 |
EP0373793A2 (en) | 1990-06-20 |
JPH02218010A (en) | 1990-08-30 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US4853080A (en) | Lift-off process for patterning shields in thin magnetic recording heads | |
US4497684A (en) | Lift-off process for depositing metal on a substrate | |
EP0234547B1 (en) | Method of manufacturing photomask and photo-mask manufactured thereby | |
EP0221093B1 (en) | Double layer photoresist technique for side-wall profile control in plasma etching processes | |
US4202914A (en) | Method of depositing thin films of small dimensions utilizing silicon nitride lift-off mask | |
US5091288A (en) | Method of forming detector array contact bumps for improved lift off of excess metal | |
EP0140817B1 (en) | Recessed metallization | |
EP0054663A1 (en) | Method for forming a copper based metal pattern | |
US4597826A (en) | Method for forming patterns | |
EP0088869B1 (en) | Thin film techniques for fabricating narrow track ferrite heads | |
US4687541A (en) | Dual deposition single level lift-off process | |
US4830706A (en) | Method of making sloped vias | |
EP0023775B1 (en) | A method of manufacturing a semiconductor device | |
US4334950A (en) | Advantageous fabrication technique for devices relying on magnetic properties | |
KR0147996B1 (en) | A method for planarization patterning onto a thin film head | |
EP0022580A1 (en) | Advantageous fabrication technique for devices relying on magnetic properties | |
KR100295669B1 (en) | Fabricating method of dual gate oxide film | |
JPS5937494B2 (en) | Thin film pattern formation method | |
JPH10256229A (en) | Manufacture of semiconductor device | |
JP2946102B2 (en) | Pattern formation method | |
JPS643337B2 (en) | ||
JPS5950053B2 (en) | Photo engraving method | |
JPS583232A (en) | Forming method for pattern | |
KR960013140B1 (en) | Fabricating method of semiconductor device | |
KR940005621B1 (en) | Method of making multi-layer resist |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: HEWLETT-PACKARD COMPANY, A CORP. OF CA, CALIFORNIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ANTHONY, THOMAS C.;REEL/FRAME:005005/0843 Effective date: 19881214 |
|
CC | Certificate of correction | ||
FEPP | Fee payment procedure |
Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
|
FPAY | Fee payment |
Year of fee payment: 4 |
|
FPAY | Fee payment |
Year of fee payment: 8 |
|
REMI | Maintenance fee reminder mailed | ||
LAPS | Lapse for failure to pay maintenance fees | ||
FP | Lapsed due to failure to pay maintenance fee |
Effective date: 20010801 |
|
STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |